Bump StyleCop.Analyzers from 1.2.0-beta.507 to 1.2.0-beta.556 (dotnet#1630)

Author: dependabot[bot]

Directory.Packages.props

@@ -19,7 +19,7 @@
     <PackageVersion Include="NuGet.Protocol" Version="6.8.0" />
     <PackageVersion Include="NuGet.Resolver" Version="6.8.0" />
     <PackageVersion Include="ObjectLayoutInspector" Version="0.1.4" />
-    <PackageVersion Include="StyleCop.Analyzers" Version="1.2.0-beta.507" />
+    <PackageVersion Include="StyleCop.Analyzers" Version="1.2.0-beta.556" />
     <PackageVersion Include="Svg" Version="3.4.6" />
     <PackageVersion Include="System.CodeDom" Version="8.0.0" />
     <PackageVersion Include="System.IO.Packaging" Version="8.0.0" />